Method for field-assisted ion exchange with anodic and cathodic contacting

ABSTRACT

An arrangement for mounting a glass member for a field-assisted ion exchange utilizing anodic and cathodic contacting by molten salts characterized by the glass member being arranged between two salt melt vessels containing the salts, each of the vessels having a contact opening surrounded by a sealing lip or surface for engaging a surface of the member as the member is interposed between the two openings and each of the vessels having an arrangement for evacuation of the vessels to form a seal between the sealing lip and the surface of the member. An embodiment of the invention includes a device for changing the level of the molten salts, either by dipping electrodes therein or by rotating the vessels so that the contact openings may be submerged in the molten salt or be above the liquid salt to allow a removing and changing of the glass members being processed.

This is a division of application Ser. No. 108,914, filed Oct. 15, 1987,now U.S. Pat. No. 4,786,391.

BACKGROUND OF THE INVENTION

The present invention is directed to an arrangement for holding ormounting a glass member for a field-assisted ion exchange with annodicand cathodic contacting by melted salts. The glass member is heldbetween two melted salt vessels, each containing the melted salt whichcontacts the glass member through contact openings fashioned in thevessels.

An arrangement for contacting a glass member is disclosed in an articlefrom Electron. Lett., Apr. 15, 1982, Volume 18, No. 8. This arrangementserves the purpose of producing a geodetic lens in a glass substratecomprising a film or layer waveguide generated by a field-assisted ionexchange. To that end, the plate-shaped glass substrate, which islocally curved in a molding cycle, has a surface held by suction againstthe sealing surface on an underside or bottom of an evacuatable cylindervessel for the one glass melt. The suctioned surface of the glasssubstrate is in contact with the glass melt in the vessel through to thecontact opening, which is surrounded by the sealing surface andsimultaneously prevents the melt from flowing out in a downwarddirection.

The underside of the suctioned glass substrate is brought into contactwith the other salt melt by dipping the substrate into this melt. Thismelt is situated in the other vessel, whose contact opening on its uppersurface is of such a size that the glass substrate can be introducedthrough it into the vessel.

Electrodes are arranged in the two salt melts, and these electrodes areconnected by electrical lines to an anode terminal and to a cathodeterminal. The electrical line of the evacuatable vessel is conductedinto the interior of the vessel from above through a vacuum-tightelectrical lead-through.

A similar arrangement is also disclosed in SPIE, Vol. 651 "IntegratedOptical Circuit Engineering III", 1986, pp. 46-50.

These arrangements, however, are unsuitable or problematical when thecontact pressure to be exerted is excessively high for the particularglass member and, for example, leads to a deformation or evendestruction of the member. For example, this can be the case givenextremely thin, plate-shaped glass members and/or when the ion exchangeis to be carried out at a temperature above the transformationtemperature T_(g) (DIN 52 24) of the glass. The relatively high contactpressure, typically 100-1,000 mbar, leads to destruction of the glassmember. However, the contact pressure, on the other hand, cannot beselected lower than about 100 mbar, since the sealing surface wouldotherwise become ineffective and would result in the emergence of thesalt melt and in a short-circuit.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an arrangement forholding a glass member for a field-assisted ion exchange with anodic andcathodic contacting by melted salts, which arrangement avoids that thecontact pressure affects the whole area of the glass member or evendestroying the glass member, particularly, even when the glass member isthin (about 1 mm or less) and/or the ion exchange is carried out abovethe transformation temperature of the glass member.

To accomplish these goals, the present invention is directed to animprovement in an arrangement for holding a glass member for afield-assisted ion exchange with cathodic and anodic contacting bymolten salt melts, wherein the glass member is arranged between two saltmelt vessels, each containing its own salt melt, said vessels havingcontact openings with one of the vessels having a sealing surface or lipbeing held against the surface of the glass member by suction as thevessel is evacuated. The improvement comprising both salt melt vesselsbeing evacuatable vessels and having sealing surfaces or lipssurrounding their openings, said sealing surfaces or rims being held onthe surfaces of the glass member by suction.

In accordance with the present invention, the glass member is held onboth vessels by suction, wherein both vessels are evacuated by a vacuum.

It has been expedient when, in accordance with the present invention,the sealing surface and contact opening of both vessels are arrangedopposite one another. The pressure exerted on the glass member by thesealing surfaces can, thereby, not have bending influence on the glassmember, but only a compressing influence. Thus, no pressure or only aslight pressure differential acts on the glass member in the region ofthe contact opening and this pressure differential is potentiallyproduced by different vacuum pressures in the two vessels.

Such a pressure differential, however, can be avoided to the greatestpossible degree when both vessels are connected to a common vaccuum pumpor source of vacuum.

A preferred modified embodiment of the arrangement of the presentinvention is that the plate-shaped member can be horizontally arranged,as herebefore, and the contacting of the underside of the member isassured by a vessel having a first section connected to a second sectionby a third section with the first section being shorter than the secondsection and forming the contacting with the glass surface and the meltin the higher second section having a level greater than the height ofthe first section.

In another preferred embodiment, the plate-shaped members can bevertically arranged and the contacting with the salt occurs from eachside. This requires that the level of the salt melt in the vessels lieshigher than the contacting opens of the vessel.

An expedient development of an arrangement of the invention is where thesalt is melted in the solid form in a container in the vessel and isthen deposited into each of the vessels. This is particularly true whenat least one of the salt containers has a shut-off valve. The valve isclosed until the molten salt in the container reaches the prescribedtemperature at which the field-assisted ion exchange is carried out.Then the valve is opened so that the molten salt melt contained in thesalt container does not come into contact with the glass member untilthis point of time. As a result, only the field-assisted ion exchangeoccurs and a thermic ion exchange, which begins when the melting pointof the solid salt is reached, will not occur. Preferably, the shut-offelement is formed in a floor of the salt container and is actuatable bya rod extending into the vessel.

The salt container in the salt melt vessel can also be constructed sothat it has a plurality of openings which will not pass the unmeltedsalt, but will allow the melted salt to enter into the salt melt vessel.By combinations of the above, the contacting of the melted salt with theglass member can be controlled.

In another embodiment, the salt is melted in the vessel out of contactwith the glass article and the vessel has means for moving the moltensalt into contact with the glass article. These means may be electrodeswhich are submerged into the salt bath to raise the level of the bath sothat it is in contact with the glass member. Thus, dipping of electrodesinto the salt melt simultaneously brings the melt into contact with theglass member as the electrodes are inserted therein.

In another embodiment, the glass member is positioned between thevessels in a position wherein the salts can be melted while out ofcontact with the glass member, and then the vessels are tilted orrotated to bring the melted salts into contact with the surfaces of theglass member.

In addition, the invention is directed to a method, wherein after thecompletion of an ion exchange process on a first glass member, thevessels are acuated to remove the salt baths from contact with a glassmember as a subsequent glass member is positioned for a subsequent ionexchange process.

Other advantages and features of the invention will be readily apparentfrom the following description of the preferred embodiments, thedrawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an embodiment of the salt meltvessel which has one of the salt melt vessels having two sections ofunequal height in communication with one another;

FIG. 2 is a schematic illustration of an embodiment of the inventionwherein each of the salt melt vessels similar to FIG. 1 contain a saltcontainer, which is filled with a solid salt;

FIG. 3 is a schematic illustration of the embodiment of FIG. 2 after themelting of the solid salt;

FIG. 4 is a schematic illustration of a second embodiment wherein thesealing surfaces and contact openings of both salt melt vessels areconstructed on the lateral side walls facing one another and whichembodiment uses dipping electrodes which are held above the level of thesolid salt filled in each vessel;

FIG. 5 is a schematic illustration of the device of FIG. 4 after meltingof the solid salt and the emersion of the dipping electrodes into thismolten salt melt;

FIG. 6 is a schematic illustration of yet another embodiment of the saltmelt vessels of the present invention which are mounted for rotation ona horizontal axis and are positioned so that the salt, during themelting in each of the vessels, is out of contact with the glass memberto be treated; and

FIG. 7 is a schematic illustration of the embodiment of FIG. 6, with thevessel being rotated to contact the glass member with the melted saltsin each vessel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principles of the present invention are particularly useful with anarrangement 100, generally indicated in FIG. 1. The arrangement 100 hasa salt melt vessel B1, which is illustrated as being a verticallymounted tube of, for example, silica glass, which has a bottom with acontact opening O1 surrounded by a circular lip or rim which is planarlyground and forms a sealing surface DF1 surrounding the opening. Theother salt melt vessel B2 of the arrangement 100 is also formed ofsilica glass bent U-shaped, which has two upwardly projecting tube legsor section B21 and B22 of unequal height, which are in communicationwith one another and are interconnected by a third section B23. The endface of an upper edge or surface OS of the smaller or shorter firstsection B21 is opened on this end to form a contact opening O2. Thecontact opening O2 is surrounded by an annular lip which is planarlygrounded and forms the sealing surface DF2 for the salt melt vessel B2.

One of the salt melt vessels, such as the vessel B1, is terminatedvacuum-tight at its upper side OSl and the other salt melt vessel B2 isterminated vacuum-tight in the upper end OS2 of its higher or largersecond section B22.

A suction line SL1 projects into the interior of the one salt vessel B1and a suction line SL2 projects into the interior of the other salt meltvessel B2. The suction lines SL1 and SL2 are connected to a suctionopening SO of a shared or common vacuum pump VP.

An electrode E1 is arranged in the interior of the salt melt vessel B1,while an electrode E2 is arranged in the vessel B2. Each of theelectrodes E1 and E2 is electrically connected to an allocated contactKK or AK, respectively, which is situated outside of the salt meltvessels B1 and B2. This electrical connection is formed by an electricalline EL, which is conducted to the interior of the given salt meltvessel B1 or B2, respectively, through a vacuum-tight electricallead-through SD.

In the embodiment illustrated in FIG. 1, every electrical line EL isformed by a movable rod St of metal and the electrical lead-through SDis fashioned as a vacuum-tight sliding lead-through, through which therod St projects into the interior of the particular salt melt vessel B1or B2 in an electrically insulated fashion. As a result thereof, theelectrodes E1 and E2 in the interior of the salt melt vessels B1 and B2and, in particular, in the salt melts S1 or, respectively S2, can bedislocated and displaced for favorable adjustment in these vessels.

An example of a vacuum-tight closure is schematically shown in FIG. 1for the upper end OS1 of the salt melt vessel B1. For example, thisclosure can be composed of a metallic cover cap KP, which is invertedover the end of the vessel or section and, for example, can be connectedto the vessel or section in a vacuum-tight manner utilizing a crimpclosure. The suction line, such as SL1, can be conducted into theinterior of the given vessel through this cap KP. The electricallead-through or sliding lead-through SD can also be arranged in this capKP. For example, it can be composed of a bushing BU of an electricallyinsulating material which is mounted in an opening in the cap KP. One ortwo O-rings R1 and R2 of elastic material is arranged in this bushing tosealingly engage a portion of the metal rod St, which is guided throughthe O-rings. Such a sliding lead-through can be used for all the vesselsof the exemplary embodiments shown in FIGS. 1-7 so that this closureand/or this sliding lead-through is shown only schematically for thesecond section B22 of FIG. 1 and for the salt melt vessels of theremaining Figures.

In each of the embodiments, it is assumed, by way of example, that thecontact AK is an anode contact and the contact KK is a cathode contact.During the operation of the arrangement of FIG. 1, a plate-shaped glassmember GK is horizontally held between the two finely grounded sealingsurfaces DF1 and DF2 of the two evacuated salt melt vessels B1 and B2.The shared vacuum pump VP, which is used for evacuating, insures thatthe same pressure is present in each of the salt melt vessels B1 and B2.The salt melt S1 contained in the vessel B1 will contact the uppersurface of the glass member GK. Since, for achieving a good contactbetween the salt melt S2 in the other salt melt vessel B2, with theunderside of the glass member GK, the level of the salt melt S2 in thehigher or second section B22 is placed higher than the level of theupper edge or end OS of the lower or first section B21. This will causethe salt melt S2 to stay in contact with the surface of the glass memberGK. The contact pressure at the sealing surfaces DF1 and DF2 must be ina range of 100-1,000 mbar. This pressure, however, now acts only at thelocation of the sealing surface and not over the entire area of thecontact opening as in previous known devices. The field assisted ionexchange can therefore also be carried out above the transformationtemperature Tg for the plate-shaped glass member which is polished onboth surfaces. In order to achieve the desired contact pressure, abacking pump can be used as the vacuum pump VP.

An embodiment of the arrangement is generally indicated at 101 in FIGS.2 and 3 and differs from the embodiment 100 in that each of the saltmelt vessels B1' and B2' are provided with salt vessels or containersSB1 and SB2, respectively. A second distinction is the structure of theelectrodes E1' and E2'. It should be noted that FIG. 2 shows thearrangement 101 in a cold condition, whereas FIG. 3 shows thisarrangement when it is in a heated condition. The cup-shaped salt vesselor container SB1 in the one or first salt melt vessel B1' is composed ofmetal and has a floor b, which is connected to the rod St. Thus, themetal container SB1 simultaneously forms an electrode E1' in this saltmelt vessel B1'. The salt container SB1 has holes L, which are formed ina circumferential wall w adjacent the floor b. The holes L have adiameter d of, for example, 2 mm, and the diameter is such that solidsalt Sz1 in the salt container SB1 will not pass through the holes whilein a cold condition. However, upon heating to a molten or melted state,the salt melt S1 will emerge through the holes L into the vessel B1'.

The salt vessel or container SB2 in the other salt melt vessel B2' isexpediently arranged in the higher or second section B22' and has avalve V. The valve V is formed by a valve opening VO in a floor b2,which valve opening VO is closed by a valve closure member VS of thevalve V. The valve closure member VS is composed, for example, of metaland is connected to the metal rod St so that it can be optionally movedback and forth from outside for closing and opening the valve V. At thesame time, this valve closure member VS forms the electrode E2' of theother or second salt melt vessel B2'. The salt container SB2 can befixed in the second section B22' and, for example, and can comprise across-partition in the second section B22', which forms the vessel floorb2 and which has an opening VO. The second section B22' is potentiallyof the same material as the cross section.

The filling of salt containers SB1 and SB2 with solid salts Sz1 and Sz2occurs in the cold condition of the arrangement. Since the saltcontainer SB1 holds back the solid salt Sz1, the sealing surface canengage a surface of the glass member GK without any problems as thesuction is applied within the chamber B1'. The filling of this othersalt container SB2 with the solid salt Sz2, which contains the exchangeion, occurs given a closed valve V so that the solid salt can, likewise,not emerge from the salt container.

After both salt melt vessels B1' and B2' have been subjected to a vacuumto draw the sealing edges DF1 and DF2 against the surfaces of the glassmember GK, the solid salts Sz1 and Sz2 are now melted by heating. Thesalt melt S1 occurring in the salt container SB1 will flow through theholes L into the salt melt SB1' to contact the glass member SK. The saltmelt Sz2 occurring in the other salt container SB2 remains in thisvessel because of the closed valve V.

When the prescribed temperature for the field-assisted ion exchangeprocess is reached, the valve V is then opened so that the salt melt S2emerges into the other salt melt vessel B2' and comes into contact withthe glass member GK, as shown in FIG. 3. What is thereby achieved isthat the field-assisted ion exchange process is not fundamentallyproceeded by a thermic ion exchange process beginning when the meltingof the solid salts Sz2 is reached.

Another embodiment of the arrangement is generally indicated at 102 inFIGS. 4 and 5. In this embodiment, two salt melt vessels B10 and B20 arecomposed of two vertical tubes, for example, made of silica glass whichare closed vacuum-tight at the upper and lower ends. The sealingsurfaces DF10 and DF20, as well as the contact openings 010 and 020,which are surrounded by the sealing surfaces, are constructed in avertical or longitudinal extending side or wall F1 and F2 of the tubeswhich lie opposite one another. To that end, each of the salt meltvessels B10 and B20 comprises a short, opened tube socket RA1 and RA2,respectively, whose finely ground end faces form the sealing surfaces orrims DF10 and DF20, respectively.

The sealing surfaces DF10 and DF20 are arranged at a distance a from afloor b3 of the salt melt vessels B10 and B20 so that a section orportion of each salt melt vessel is below the sealing surfaces. Thesesections are initially filled with the solid salts Sz1 or Sz2,respectively.

Vertically movable, block-shaped dipping electrodes E10 and E20 are alsoarranged in the salt melt vessels B10 and B20. These electrodes areconnected to contacts KK an AK, respectively, by a vertically movablemetal rod such as ST. In this way, these rods also form electrical linesEL for the dip electrodes, and project into the interior of the saltmelt vessels through vacuum-tight sliding lead-throughs SD.

After the sections of the two salt melt vessels B10 and B20, which aresituated under the sealing surfaces DF10 and DF20 have been filled withthe allocated solid salts Sz1 and Sz2, respectively, in the coldcondition, the sealing surfaces DF10 and DF20 are firmly sealed againstboth sides of a plate-shaped and vertically arranged glass member GK byapplying suction to each of the vessels B10 and B20. While forming thisvacuum seal, the dipping electrodes E10 and E20 are arranged in thewithdrawn position illustrated in FIG. 4.

The solid salts Sz1 and Sz2 are melted by heating and the level of themelted salts S1 and S2 remain under the sealing surfaces DF10 and DF20.The lowest portion of each of the sealing surfaces DF10 and DF20 have alower level r1 (FIG. 5), which is also the lower level of the contactopenings 010 and 020.

As soon as the prescribed temperature for the ion exchange process isreached, the two dipped electrodes E10 and E20 are simultaneously dippedinto the respective salt baths S1 and S2 so that the level N (FIG. 5) ofthe salt melts rises. The dipped electrodes E10 and E20 are dimensionedin terms of volume so that the level N rises to such a degree that themolten salt of the salt melt covers the openings 010 and 020 and thatthe glass member GK comes into contact with the melts on both surfaces.In particular, the eletrodes are dimensioned so that the level N risesabove an upper limitation r2 of the contact openings 010 and 020,respectively (FIG. 5). While in this condition illustrated in FIG. 5,the field assisted ion exchange can begin in this way without having anypreceding undersirable thermic ion exchange.

After the conclusion of the ion exchange, the two electrodes can belifted so that the two salt melts S1 and S2 will then retreat or retractinto the vessel sections lying under the sealing surfaces DF10 and DF20.After that, the interior of the two evacuated salt melt vessels B10 andB20 can be brought into ambient pressure, for example, to atmosphericpressure, and the glass member GK can be taken from the mount or holder.Since the retracted salt melts S1 and S2 are still available for furtherion exchange processes on a subsequent glass member or specimens, thearrangement of 102 of FIGS. 4 and 5 is advantageously suitable for massproduction. For example, waveguides or waveguide structures manufactureon the basis of an ion exchange method.

An embodiment of the fourth arrangement is generally indicated at 103 inFIGS. 6 and 7 and also provides the advantage of the embodiment of thearrangement 102. The arrangement 103 essentially differs from thearrangement of 102 in that the two salt melt vessels B10' and B20' canbe rotated --for example through 180°--around a horizontal rotationalaxis A, that passes through the midpoint of each vessel, between anerect working position shown in FIG. 7 into an upside-down positionshown in FIG. 6. In addition, an upper edge of each of the contactopenings 010' and 020' of the salt melt vessels B10' and B20' arearranged at a distance 1 from the axis A, which has a height h from eachend of each vessel B10' and B20'. The level N of the salt melts S1 andS2 in the salt vessels B10' and B20' is set so that it lies at least ata height of h-1 and, at the most, by a height slightly less than h whenin the working position.

In the position of FIG. 6, the salt melt vessels B10' and B20' arefilled with the solid salts and have a suction applied to draw the glassmember GK firmly against the sealing surfaces DF10 and DF20. After thesalt melts S1 and S2 have been produced by heating the solid salts andwhen the prescribed temperature for the field-promoted ion exchangeprocess has been reached, the arrangement 103 is then rotated through180° to the working position illustrated in FIG. 7. As a result thereof,both sides of the glass member GK simultaneously come into contact withthe salt melts as in the previous arrangement 102 of FIGS. 4 and 5.Whereupon the field assisted ion exchange process can begin withouthaving been preceded by any undersired, thermic ion exchange.

The above-defined setting of the level N assures that the contactopenings 010' and 020' in the working position are entirely immersed inthe salt melt, whereas they are not in contact with the salt melt in theposition of FIG. 6. In addition, the electrodes e1 and e2 need not befashioned as large volume, dipped electrodes, as in the arrangement 102of FIGS. 4 and 5. The electrodes e1 and e2 can also be arrangedhorizontally displaceable, as shown in FIGS. 6 and 7. The horizontaldisplaceable electrodes are also favorable for this arrangement. Likethe vertically displaceable electrodes, the horizontally displaceableelectrodes e1 and e2 can also be connected to the contacts AK and KK byhorizontal, movable metal rods St, whereas the rods project into theinterior of the salt melt vessels B10' and B20' through vacuum-tightsliding lead-throughs SD. The suction lines SL1 and SL2 areadvantageously arranged coaxially with the rotational axis A.

The salt containers, particularly the salt containers comprising theshut-off elements in the arrangement of 101 of FIGS. 2 and 3 can also beemployed in the arrangement 102 of FIGS. 4 and 5.

In all of the embodiments shown and set forth above, the slidinglead-through SD formed both the electrical as well as mechanicallead-throughs. However, electrical and mechanical lead-throughs couldalso be realized separately from one another.

Althrough various minor modifications may be suggested by those versedin the art, it should be understood that I wish to embody within thescope of the patent granted hereon all such modifications as reasonablyand properly come within the scope of my contribution to the art.

I claim:
 1. In a method for a field-assisted ion exchange with anodicand cathodic contacting with a molten salt melt comprising the step ofproviding an arrangement including two vessels, each of said vesselshaving a contact opening with a sealing rim for engaging oppositesurfaces of a glass member to be treated, means for changing the levelof the molten salt in each vessel from a level removed from the contactopening to a level covering the entire contact opening of each vessel,and means for applying a vacuum to the interior of each vessel, loweringthe level of the molten salts to not cover the openings, positioning aglass member between the two openings, creating a vacuum in each vesselto form a seal with the sealing rim of each opening, then raising thelevel of the molten salts to cover the openings, treating the members byconducting the ion exchange, then at the completion of treating themembers by the ion exchange lowering the level, removing the treatedmember, positioning a second member and repeating the process ofcreating a vacuum, raising the level of the molten salt in each vesseland treating the member by conducting a field-assisted ion exchange witha cathodic and anodic contacting.